This disclosure relates generally to methods and systems for steganographically embedding information, and more particularly to a system and method for utilizing a multiple color overlay to embed infrared information in documents and/or images collocated with human visible information.
Current digital document counterfeit prevention systems are mainly based on the use of digital watermarks, a technique which permits the insertion of information (e.g., copyright notices, security codes, identification data, etc.) to digital image signals and documents. Such data can be in a group of bits describing information pertaining to the signal or to the author of the signal (e.g., name, place, etc.). Most common watermarking methods for images work in spatial or frequency domains, with various spatial and frequency domain techniques used for adding watermarks to and removing them from signals.
For spatial digital watermarking the simplest method involves flipping the lowest-order bit of chosen pixels in a gray scale or color image. This works well only if the image will not be subject to any human or noisy modification. A more robust watermark can be embedded in an image in the same way that a watermark is added to paper. Such techniques may superimpose a watermark symbol over an area of the picture and then add some fixed intensity value for the watermark to the varied pixel values of the image. The resulting watermark may be visible or invisible depending upon the value (large or small, respectively) of the watermark intensity.
Spatial watermarking can also be applied using color separation. In this approach, the watermark appears in only one of the color bands. This type of watermark is visibly subtle and difficult to detect under normal viewing conditions. However, when the colors of the image are separated for printing or xerography, the watermark appears immediately. This renders the document useless to the printer unless the watermark can be removed from the color band. This approach is used commercially for journalists to inspect digital pictures from a stock photo agency before buying un-watermarked versions.
Alternatively, another approach uses infrared (IR) ink rendering to encode a watermark that is not visible under normal illumination, but revealed under IR illumination to a suitable infrared sensitive device such as a infrared sensitive camera. The traditional approach, often used, is to render a watermark with special infrared (IR) inks and to subsequently identify the presence or absence of the watermark in a proffered document using simple infrared illumination and sensing. However, these inks are costly to employ, generally requiring additional workflow steps, and as a result are typically economically viable only in offset printing scenarios, and therefore only truly avail themselves to long print runs. Additionally, these materials are often difficult to incorporate into standard electrophotographic or other non-impact printing systems like solid ink printers, either due to cost, availability or physical/chemical properties. This in turn particularly discourages their use in variable data printing arrangements, such as for redeemable coupons, for example.
There is well established understanding in the printing industry regarding the utilization of infrared material inks in combination with infrared light sources and sensors as employed for security marks, particularly as a technique to deter counterfeiting. However, there remains a long standing need for an approach to such a technique which will provide the same benefit but with lower complexity and cost, particularly in a digital printing environment, using only common consumables.
All U.S. patents and published U.S. patent applications cited herein are fully incorporated by reference. The following patents or publications are noted:
U.S. Patent Application Publication No. 2005/0078851 to Jones et al. (“Multi-channel Digital Watermarking”) describes a system for providing digital watermarks through multiple channels. The channels can include visible, ultraviolet and infrared channels. The non-visible channels can be selected to respond either in the visible or IR/UV spectrums upon the appropriate illumination in the infrared or ultraviolet spectrums. The watermarks in the various multiple channels can cooperate to facilitate watermark detection or to authenticate an object in which the watermarks are embedded.
U.S. Pat. No. 7,127,112 to Sharma et al. (“Systems for Spectral Multiplexing of Source Images to Provide a Composite Image, for Rendering the Composite Image, and for Spectral Demultiplexing of the Composite Image by Use of an Image Capture Device”) provides methods and systems for spectrally-encoding plural source images and for providing the spectrally-encoded plural source images in a composite image, for rendering the composite image on a substrate, and for recovering at least one of the encoded source images from the rendered composite image. A desired source image is recovered when the rendered composite image is subjected to illumination by one or more illuminants and the desired source image is detected by one or more sensors in an image capture device. The spectral characteristics of the colorants, illuminants, and sensors are employed to spectrally encode the source image in the composite image.
The disclosed embodiments which follow below provide examples of improved solutions to the problems noted in the above background discussion and the art cited therein. There is shown in these examples a method for creation of an infrared mark with distraction pattern to be printed by a printing device as an image on a substrate for embedding information in printed documents. The method comprises providing a substrate reflective of infrared, and selecting at least one background color mixture for the infrared mark. The method also teaches selecting at least one foreground color mixture for the infrared mark, the at least one foreground color mixture exhibiting low contrast against the at least one background color mixture under normal illumination, and high contrast against the at least one background color mixture under infrared illumination. The method further comprises selecting at least one distraction color mixture for the infrared mark. This at least one distraction color mixture is comprised of at least two colors. The at least one distraction color mixture as selected has a substantially negligible effect on the infrared response of the foreground and background color mixtures, as well as having a substantially noticeable effect of the visual response of the least one foreground color mixture and the least one background color mixture. The method also comprises creating an infrared mark using the foreground color mixture against the background color mixture, and creating a distraction pattern using the distraction color mixture as collocated with the infrared mark.
In yet another embodiment there is disclosed a method for creation of an infrared mark to be printed by a printing device as an image on a substrate for embedding information in printed documents. The method comprises providing a substrate reflective of infrared and selecting at least one background color mixture for the infrared mark. The method further comprises selecting at least one foreground color mixture for the infrared mark, the at least one foreground color mixture exhibiting low contrast against the at least one background color mixture under normal illumination, and high contrast against the at least one background color mixture under infrared illumination. The method further comprises selecting at least one distraction color mixture for the infrared mark, the at least one distraction color mixture comprised of at least two colors, the at least one distraction color mixture having a substantially negligent-negligible effect on the infrared response of the foreground and background color mixtures, as well as having a substantially noticeable effect of the visual response of the least one foreground color mixture and the least one background color mixture. The method thus creating an infrared mark using the foreground color mixture against the background color mixture in close spatial proximity, with a distraction pattern using the distraction color mixture as collocated with the foreground color mixture against the background color mixture.
In an alternate embodiment there is disclosed a system for an infrared mark as rendered by a conventional printing device as an image on a substrate comprising a substrate reflective of infrared with at least one background color mixture for the infrared mark and at least one foreground color mixture for the infrared mark, the at least one foreground color mixture exhibiting low contrast against the at least one background color mixture under normal illumination, and high contrast against the at least one background color mixture under infrared illumination. The embodiment further includes at least one distraction color mixture for the infrared mark, the at least one distraction color mixture comprised of at least two colors, the at least one distraction color mixture having a substantially negligible effect on the infrared response of the at least one foreground and background color mixtures, as well as having a substantially noticeable effect of the visual response of the at least one foreground color mixture and the at least one background color mixture. Thus an infrared mark is created by using the at least one foreground color mixture imaged as arranged in close spatial proximity against the at least one background color mixture, with a distraction pattern imaged using the at least one distraction color mixture as collocated with the at least one foreground color mixture in close spatial proximity against the at least one background color mixture.
In a further embodiment there is disclosed a method for creation of an infrared mark to be printed by a printing device as an image on a substrate for embedding information in printed documents. The method comprises providing a substrate reflective of infrared, selecting at least one background color mixture for the infrared mark and selecting at least one foreground color mixture for the infrared mark, the at least one foreground color mixture exhibiting low contrast against the at least one background color mixture under normal illumination, and high contrast against the at least one background color mixture under infrared illumination. The method further includes selecting at least one distraction color mixture for the infrared mark, the at least one distraction color mixture comprised of at least two colors, the at least one distraction color mixture having a substantially negligible effect on the infrared response of the foreground and background color mixtures, as well as having a substantially noticeable effect of the visual response of the least one foreground color mixture and the least one background color mixture. The method also comprises printing the image background with the at least one background color mixture, along with printing the image foreground with the at least one foreground color mixture, and overprinting a distraction pattern with the at least one distraction color mixture to create an infrared mark using the at least one foreground color mixture against the at least one background color mixture, with a distraction pattern using the at least one distraction color mixture as collocated with the at least one foreground color mixture against the at least one background color mixture.